The present invention relates to an open-center system for providing pressurized fluid to at least a main load circuit (fluid pressure operated device) and more particularly, to such a system including a fluid controller which defines a main fluid path and an auxiliary fluid path.
In many vehicle hydraulic systems, there are two primary load circuits, or fluid pressure operated devices. One is the hydraulic steering cylinder, and the other is some sort of auxiliary device, such as a lift cylinder or winch motor, etc.
In such systems, it is conventional to have a single pump for both load circuits to minimize the expense of the hydraulic system. In addition, the system would include a main steering control unit, to control the flow to the steering cylinder, and an auxiliary valve to control the flow to the auxiliary device. In addition to the cost of two separate valves, such a system would require some sort of control or interface between the valves because, typically, the steering circuit must be given priority over the auxiliary circuit, for safety purposes. Therefore, if the auxiliary device is being operated, and the vehicle operator initiates steering, flow to the auxiliary circuit must be interrupted, so that there is sufficient pressurized fluid available to the steering circuit. The need for such interface controls would make a system of the type described quite expensive and complicated.